SCG has a 20% stake in Binh Minh Plastic JSC and nearly 25% stake in Tien Phong JSC, who together hold half the market share in the plastic building materials market.

SCG and many other Thai firms are continuing to acquire stakes in plastics companies.

Tran Viet Anh, chairman and general manager of Nam Thai Son Co and deputy chairman of the HCM City Rubber - Plastic Manufacturers Association, said the country has nearly 3,000 plastics companies, 99.8% of them privately held.

Thai companies are primarily aiming at the top 100 firms, he said.

In many cases domestic firms show signs of declining production and business capacity, lack the confidence to take on the new foreign rivals, and end up agreeing to sell out when foreign investors offer high prices for their stakes, he said.

Ho Duc Lam, chairman of the Vietnam Plastics Association, said by increasing investment in the country’s plastic industry, Thai firms hope to both exploit the lucrative domestic market and take advantage of free trade agreements that Vietnam has signed.

The plastics industry is one of the fastest growing in Vietnam, expanding annually at 16-18% in 2010-15, Lam, who is also chairman of Rang Dong Plastic joint Stock Company, said.

But with the annual plastic consumption per capita in Vietnam at just 41kg, much lower than in other countries, the prospects remain huge, he said.

Anh said Thai firms only pay 1% or even 0% interest on bank loans for certain projects, while Vietnamese firms have to pay 6-7%, making it hard for them to compete with the Thais.